<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <button id="btn" disabled onclick="tiao()">同意(100)</button>
</body>
<script>
    var num = 99;
    function show() {
        var btn = document.getElementById("btn");
        btn.innerHTML = "同("+num+")意";
        num--;
        if(num%5==0){
            btn.disabled = false;
        }else{
            btn.disabled = true;
        }
        if(num==0){
            clearInterval(r);
            btn.innerHTML = "同意";
            btn.disabled = false;
        }
    }
    var r = setInterval("show()",100);
    function tiao() {
        location.href = "login.html";
    }
</script>
</html>